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1、 A national laboratory of the U.S. Department of Energy Office of Energy Efficiency 7502 h exposure in an Atlas XR-260 WOM (providing 1.9 years equivalent outdoor exposure) results in an increased modulus, implying increased stiffness and consequent loss in impact strength. Measurements were made at
2、 a tortional frequency of 10 rad/s over a wide temperature range (-25 to 75C). 1 Further interactions have been held with material suppliers to identify several new types of samples that have the potential to preclude the thermal bonding problem. GE Plastics, a major supplier of PC sheet, is interac
3、ting with Polymer Extruded Products to provide thermally-bonded Korad/PC samples. The UV screening layer is thicker than previously used (0.08- 0.15 mm thick rather than 0.05 mm thick), and enhanced screening films (that provide twice as much UV absorption as previously tested) are incorporated into
4、 their laminate samples. PPG and Bayer have supplied samples in which UV-absorbing organic clear coats are applied to PC sheet. Such constructions are used in automotive headlamp applications. If a UV- screening film cannot be thermally bonded to PC sheet as it is extruded and/or cannot avoid severe
5、 adverse thinning during thermoforming, then clear coats could be applied to thermoformed PC to avoid such damaging effects to the screening agent. Long term testing and evaluation of these new material samples is underway. 3.2 Absorber Materials Solar manufacturers have recently considered unglazed
6、 constructions in which the polymeric absorber is exposed to UV sunlight. Consequently, we have emphasized the effect of UV exposure on mechanical properties of polymer absorbers. One candidate material is metallocene-based multi-density polyethylene (MBMDPE). We have measured mechanical properties
7、of this material as a function of exposure to UV light in our Ci5000 WeatherOmeter. The most sensitive parameter is % strain at break. A three-fold loss in % strain at break is evident after exposure to a cumulative dose of UV irradiance equivalent to 4 years exposure in Miami, FL (Fig. 2). As long
8、as a reasonable residual strain at break is retained (i.e., does not drop to near zero), the absorber material is useable. For the length of time tested, MBMDPE seems suitable as an absorber material. Longer term testing and evaluation of MBMDPE is being continued. 4. Conclusions We have interacted
9、with several major polymer manufacturers to identify polymeric glazing constructions that can potentially overcome drawbacks associated with previously promising materials. Samples have been prepared and are under test. Loss of mechanical properties have been measured for glazing samples exposed to
10、UV light, providing further impetus to demonstrate stable UV screening constructions. UV weathering of polymeric absorbers also results in loss of mechanical properties. However, if a reasonable residual strain at break is retained, the absorber material is useable. Testing of candidate polymeric ab
11、sorber materials is continuing. ACKNOWLEDGEMENTS The authors would like to thank Michael Kempe at NREL for assistance with the DMA measurements and for many useful discussions. We would also like to thank Jay Burch at NREL for his support and thoughtful deliberations. This work was performed under D
12、OE contract DE-AC36-99-GO10337. REFERENCES 1Solar Energy Technologies Program Multi-Year Technical Plan, 2003-2007 and Beyond, DOE/GO- 102004-1775, U.S. Department of Energy, Washington DC, January 2004. DOE/GO-102004-1775, 166 p. Web Link: www.nrel.gov/docs/fy04osti/33875.pdf 2 J.H. Davidson, S. C.
13、 Mantell, and G. J. Jorgensen, “Status of the Development of Polymeric Solar Water Heating Systems,” Advances in Solar Energy, An Annual Review of Research and Development, Vol. 15, D.Y. Goswami, Ed., American Solar Energy Society, Inc., Boulder, CO, 2003, pp. 149-186. 0.8 0.9 1.0 1.1 1.2 1.3 1.4 -3
14、0-20-1001020304050607080 Temperature (C) G (GPa) Weathered Unweathered Fig. 1. Shear modulus as a function of temperature for accelerated weathered (1.9 years equivalent outdoor exposure) vs. unweathered thermal- bonded Korad(R)/PC 0 50 100 150 200 01234567 Time of Ci5000 Exposure (mo) Strain at Bre
15、ak (%) 1 Year in Miami, FL 2 Years in Miami, FL 3 Years in Miami, FL 4 Years in Miami, FL Fig. 2. Strain at break of MBMDPE as a function of Ci5000 exposure 2 REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 The public reporting burden for this collection of information is estimated to aver
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